Dental Crowns

Dental CrownsSynonyms : Jacket, Jacket Crown, Crown Restoration, Cap
A dental crown is a dental restoration that covers a tooth to restore it to its normal shape, size and function. Its purpose is to strengthen or improve the appearance of a tooth.

A dental crown can
– restore a tooth when there isn’t enough tooth remaining to provide support for a large filling
– attach a bridge to replace missing teeth
– protect weak tooth from fracturing
– restore a fractured tooth
– cover a badly shaped or discolored teeth
– cover a dental implant

Lithium disilicate jacket crown. Photo credit: Dr. Jesus Lecitona

What is it made from?
The look and function of a crown are considered when choosing the material ideal for your case.
Crowns are made from several types of materials: metal alloys, porcelain, composite resin, acrylic resin or combinations of these materials.

Types of Crowns

Stainless steel crowns can be prefabricated and can also be custom-made. They are used on permanent teeth primarily as a temporary measure. They are used in primary dentition to protect the teeth of a child at high risk for tooth decay, especially when a child has difficulty keeping up with everyday oral hygiene.

Metal crowns can be made of gold alloy, base-metal alloy (e.g. nickel or chromium) and other alloys (e.g. palladium). Compared with other crown types, less tooth tissue needs to be removed with metal crowns, and tooth wear to opposing teeth is minimal. Metal crowns can withstand great occlusal and masticatory forces well and lasts long in terms of wear down.

Metal ceramic, also called as porcelain fused to metal, crowns are the conventional and most commonly used dental crowns. It utilizes the bond between porcelain and metal that is achieved at high temperatures. Enough space is needed from tooth prep for the opaque porcelain, dentin and enamel porcelain to create the appearance.

High strength core crown consists of 2 layers. The dental crown’s strength is derived from the inner core made from Inceram, and overlaid with conventional porcelains to improve the esthetics. Inceram is a glass and alumina material.

Fine alumina powder is applied to an absorbent refractory die and any residual pores are filled with molten glass to produce a dense, crystalline core structure. The core has high strength and elastic modulus. The high content of alumina makes it resistant to acids making adhesive bonding difficult.

Pressed-glass ceramic crowns comprise 2 layers, an inner material made from Empress or E.max and an outer layer made from conventional (feldspathic) porcelains. The outer layer is thinner than in hign strength core crowns. This is to improve the surface finish and characteristics. The core is made using the lost wax technique. Wax is applied to a phosphate-bonded investment, after burnt-out, leucite reinforced glass ceramic is pressed under pressure into the space.
Milled Zirconia dental crowns. Photo credit: Dr. Jesus Lecitona
Milled Zirconia dental crowns. Photo credit: Dr. Jesus Lecitona

In milled-porcelain core crowns, computer controlled technology is used to mill the coping. The ingot is made from zirconia. Aside from zirc ingots, other types of ingots are also used, such as aluminum oxide etc. The outer surface is made from conventional porcelain. Conventional porcelain is overlaid onto the core which is responsible for the improved translucency.

Milled Zirconia dental crowns. Photo credit: Dr. Jesus Lecitona

Capillary technique (Captek) dental crown‘s basic structure is similar to metal ceramic crowns except that the core is made from a precious metal. Captek have improved marginal fit and biocompatibility. The appearance is warmer compared to conventional PFM crowns because the yellow color from the gold core reflects the light. Captek requires less tooth reduction.